Field of the Invention:
Scrap metal is predominantly melted in electric arc furnaces for steel production. Above all electric arc furnaces which use 100% scrap metal generate network disturbances, for which the affected power supply company frequently charges with contractual penalties if specific limiting values are exceeded. Therefore, compensation systems (SVC—static VAR compensator) are installed in steel mills, to reduce network disturbances such as flicker and harmonics, in order to maintain predefined limiting values. However, such SVC systems only react afterwards to the already generated network disturbance from the harmonics or flicker generated in the electric arc furnace during the scrap metal melting, and cannot always maintain the prescribed limiting values, in particular if the electric arc furnaces are operated on weak supply networks.
Various conventional remedying measures are known for avoiding excessively high flicker values. For example, a low flicker melting operation is proposed, in which an appropriately selected scrap metal mix having an ultralow KSt value, auxiliary reactants in the furnace loop and a control-technology parameterization are used for the arc stabilization. In this case, the KSt value is the value which describes in particular the type, weight, and density of the scrap metal. According to UIE, this value is between 48 and 85. For example, a furnace transformer restrictor can be used as an auxiliary reactant in the furnace loop. In addition, so-called compensation systems (SVC) have conventionally been used for decades, with which the generated flicker can be reduced by approximately half. Conventional SVC systems having voltage source inverters based on IGBTs (insulated gate bipolar transistor) are also known, which are used if the flicker reduction is to be more than doubled.
However, these conventional measures are linked either to high investment and operating costs or to losses in the production. Not only do the scrap metal composition and quality have influence on network disturbances, the regulation performance of the electrode regulation and the mode of operation in the scrap metal melting phase can also have noticeable effects on the generation of network disturbances. The recognition of scrap metal movements and scrap metal collapse is thus substantially left to the operating personnel. A conventional electrode regulation can only react afterwards to these events here. Only conventional approaches are known, which engage afterwards in the steel production process. Accordingly, a conventional compensation system can only react to the states during the melting and the predefined limiting values are then often exceeded.